This application claims the priority of Korean Patent Application No. 2002-31606, filed Jun. 5, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to the field of digital signal processing (DSP) system, and more particularly, to an integer coding method supporting diverse frame sizes and a coder-decoder (CODEC) implementing the method.
2. Description of the Related Art
A digital signal processing (DSP) coder-decoder (CODEC) may be used to perform digital signal arithmetic operations in devices which provide multimedia content.
Floating-point operations are used very frequently in DSP algorithms. Also, when DPS algorithms are used to improve speed or are applied to a platform, floating-point operations are transformed into integer operations. Here, integer coding means that a floating-point operation on a CODEC is transformed into a fixed-point operation.
DSP CODECs, used with most forms of multimedia including video and audio, use the characteristics of a frequency region by employing discrete cosine transform (DCT) or discrete Fourier cosine transform (DFT). Here, DCT and DFT use fast Fourier transform (FFT) for high-speed operation. In the algorithm of FFT, multiplication operations are used. Thus, the result of FFT is very sensitive to input parameters during an integer coding operation.
FIG. 1 is a flowchart illustrating a conventional integer coding method employing an inverse discrete Fourier transform (IDFT).
First, samples in units of frames input in the form of a variable length code (VLC) are inversely quantized to generate samples having real number values (110). Subsequently, the inversely quantized samples are multiplied by 2n according to a maximum sample value and an effective bit (120). Here, the maximum sample value is a sample value having the largest absolute value among all sample values. As shown in FIG. 2, an effective bit region 210 is obtained by combing a symbol bit region S, an integer bit region 220, and a decimal bit region 230. And, n is determined by subtracting a maximum value bit from the effective bit region 210.
Subsequently, an IDFT operation is performed on the samples multiplied by 2n (130).
In the conventional integer coding method illustrated in FIG. 1, when frames on which the IDFT operation is performed have different number of samples, a multiple to be multiplied by samples is determined according to the maximum sample value and the effective bit of the largest frame. Also, the multiple is fixedly applied to a frame having fewer samples than the largest frame. Thus, in the conventional integer coding method, when an integer operation of a frame having relatively fewer samples is performed, the decimal bit region 230 is fixed. Thus, the remaining part of the integer bit region 220 cannot be utilized, and accuracy during an integer coding operation is lowered.